Electrostatic discharge (ESD) is a natural phenomenon occurring frequently in daily life. ESD can generate a large current in a short period of time. For example, a human body model (HBM) electrostatic discharge usually occurs within several hundreds of nanosecond, with a peak current of several amperes. Electrostatic discharge of some other modes, such as a machine model (MM) and a charged device model (CDM), may occur in a shorter period of time and may have a larger current.
When the large current generated by the ESD passes through an integrated circuit in a short period of time, it may result in a power consumption much higher than what the integrated circuit can bear, causing physical damage to the integrated circuit and, possibly, circuit failure. In fact, ESD has become a major factor that causes failure of integrated circuits during their manufacture and use.
In practice, two approaches have been followed to reduce or prevent damage caused by ESD: the environment and the circuit itself. With regard to the environment, the approach mainly involves reducing the production of static electricity and timely removing the generated static electricity, such as using materials that do not easily generate static electricity, increasing the environment humidity, or grounding operators and/or apparatuses. With regard to the circuit, the approach mainly involves improving the ESD resistivity of the circuit, such as by using an ESD protection device or circuit to protect the internal circuit from ESD damages.
With regard to using an. ESD protection device, a trigger voltage of the ESD protection device should be lower than that of the device being protected. The ESD protection device should also have a capability of discharging current. In addition, the DC breakdown voltage of the ESD protection device should be higher than the power source voltage. The ESD protection device should meet such conditions so as to not impact the operation of the device being protected. To avoid a problem of latching up, a holding voltage of the ESD protection device should be higher than the power source voltage.